The invention relates to a method and to correspondingly designed apparatus for processing components in which a molten phase is produced by local energy input. In this regard, the invention can be used in conjunction with known thermal soldering, welding and cutting methods.
During known welding and cutting methods, a molten phase is produced locally in a controlled way by energy input. Intense substance movements, which are caused, inter alia, by the so-called Marangoni effect, take place inside the melt that is formed. The intensity depends on the respective materials, the energy density and the resulting temperature gradients. This effect is due to the surface tension of the materials which is influenced as a function of temperature. This effect is, in particular, caused and influenced by large temperature gradients as a result of very high energy intensities, as are encountered especially in the case of laser beams, electron beams or plasma beams.
Owing to high shear stresses at the surface of the molten phase, speeds of the substance movement of the order of about 1 m/s occur. Since it has, to date, been very difficult to influence these processes, it was necessary to accept surface irregularities such as burnt-in notches, which occur at the section edges when the melt re-solidifies during welding or re-melting, and also pore formation during welding.
In the case of thermal cutting methods, such as e.g. laser-beam cutting, an intense gas jet expels the locally produced melt from the section join that is formed. When this happens, grooves are formed at the cut edges and, in many applications, necessitate mechanical finishing of the cut edges.
In the case of thermal cutting, it is further necessary to provide for the fact that the capillary forces and the surface tensions are correspondingly increased in a narrow section join, and correspondingly higher resistances oppose the ejection of the melt from the section-join region. Consequently, the cutting process is substantially influenced by the nozzle configuration and the gas stream used, i.e. the gas speed or the respective flow rate. This predominately affects the processing rate that can be achieved, and imposes corresponding limits for the high-speed cutting, especially when cutting thick sheet metal.
The object of the invention is to provide a method and correspondingly designed apparatus which can improve the quality of the weld beads and cut edges that are formed, and which can increase the processing rate.
According to the present invention, this object is achieved by imparting oscillations having a frequency above 15 kHz to at least one of the components or work pieces that is being welded, soldered or cut, or to the region of the molten phase existing during the welding, soldering or cutting, or to a filler material that is being added to the region of the molten phase. The molten phase can be produced by a local energy input using at least one of the group consisting of an electric arc, a jet of combustible gas, an electron plasma, and a laser beam.
According to the invention, the oscillations are imparted to the work piece or to one or more components to be bonded together or a filler material, such as e.g. a filler wire, a solder or a powder. The oscillations have a frequency above 15 kHz and are preferably oscillations in the ultrasonic range. The effect thereby achieved is that these oscillations also act in the molten phase and can reduce its surface tension. The invention can be used in a wide variety of thermal soldering, cutting, welding, coating and re-melting methods, and it can have advantageous effects especially in methods where high energy densities can be achieved. The methods can also be implemented simultaneously in combination with one another, wherein at least two different energy sources being used.
The oscillations can be stimulated in a work piece component, or in the molten phase, and can be produced in various ways that will be discussed more fully below.
Using the invention, for example in the case of thermal cutting methods, such as e.g. laser-beam cutting, the melt ejection is significantly facilitated and it is consequently possible to work with a lower gas pressure while still achieving the same or even a higher processing rate. Furthermore, the groove formation which has already been mentioned in the description of the prior art is significantly reduced, so that mechanical finishing of the cut edges becomes unnecessary in many cases. Furthermore, using the invention, the so-called whisker adhesion on the components is eliminated or at least largely avoided.
In thermal welding methods, a more uniform and pore-free weld bead is formed, and the interfaces between the weld bead and the component substrate can likewise be formed more homogeneously and consequently with better mechanical properties as well, especially in terms of strength. The surface of the weld bead or weld track is also formed more smoothly.
The oscillations stimulated in the component can be produced using at least one oscillator or transducer, which, for example, employs the piezoelectric effect. Such a transducer can be installed immediately on the surface of the component, and the oscillations excited in it can thus be injected into the component. It may be preferable for a liquid film to be formed between the component surface and the transducer to improve the coupling.
Such a transducer can also be arranged on a clamping device for clamping components of the work piece that are to be correspondingly processed, or can be integrated in such a clamping device, so that various component formats can also be readily influenced according to the invention. It is, of course, also possible to use more than one such transducer, in which case it will generally be expedient to operate them in such a way that the oscillations applied from the various transducers do not lead to any substantial amplitude reduction. In that case, the different distances of the respective transducers from the molten phase, which is currently being formed, and the respective speed of sound in the component, should be taken into account.
If the injection of the oscillations does not take place via the component substance and their propagation through the component, it may be expedient for the injection of the oscillations to take place in the immediate vicinity of the molten phase. In this way, attenuation effects can be substantially minimized.
For instance, it may be expedient to inject oscillations not directly using an transducer, but via a coupling element, which can for example be a moving roller or a wheel to which oscillations are correspondingly applied. Such a roller or wheel can be moved along the component surface, even underneath it, so that it is possible to maintain a relatively small and constant distance from the molten phase that is formed, even when there is corresponding relative movement between the component and the current location of the energy input. For example, such a roller can be rigidly connected to a processing head, e.g. a laser-processing head, which is moved over the component.
It may furthermore be favorable if a component to be correspondingly processed is at least partially immersed in a liquid. The component can then be half-surrounded or fully surrounded by a liquid, as is the case, e.g., when cutting under water.
Another possible way of injecting oscillations is for oscillations to be imparted to a filler material that is added, which can be a filler wire or an electrode as are already employed in welding methods. The injection of sound can also be used to influence the dripping of the filler wire, e.g., during electric arc welding wherein it is possible in particular to form smaller drops. However, injection of the oscillations can also be carried out by using powder or flux that is added or by using a solder.
Another possible way of generating forced oscillation in the component and/or in the molten phase is to direct an oscillating jet of liquid at the component surface, in which case a corresponding frequency should be selected. By way of example, a corresponding oscillation can be superimposed on the stream of shielding or cutting gas which is directed at the component surface, particularly in the region of the molten phase, so that the desired effect can likewise be achieved in this way.
The generation of oscillations in the favorable frequency range can also be achieved by correspondingly controlling the power of a laser beam. In this case, the power is periodically increased in pulses and then oscillations develop in the resonator of the laser-light source, so that short intense laser-beam pulses are directed at the component that is to be processed that cause short-term evaporation of the material surface, and consequently an elevated pressure on the molten phase. In the event that no evaporation takes place, the correspondingly created heat sources can also cause a comparable effect. If a laser-light source in the form of a CO2 laser is employed, an oscillating resonator mirror, which oscillates in the desired frequency range, can utilized with this laser-light source.
Another possible way of generating the desired oscillations, at least in the region of the molten phase, can also be achieved by transmitting oscillations through the surrounding air. For example, an transducer in the form of an ultrasonic transmitter can be excited at a selected distance from the component surface. Such an ultrasonic transmitter should preferably be able to direct a relatively narrow sound cone at the molten phase.
The energy required for exciting the oscillation can, for example, be reduced by selecting a frequency at which resonance takes place in the molten phase. Since, in this case, substance-specific conditions not only have an influence but also may change during the processing, it is preferable to work with oscillations within a predetermined frequency interval, which is successively swept through, so that the excitation is carried out at various frequencies within this interval.
Another similar possible way is to use oscillations having component-specific wavelengths, at which constructive interference takes place in the respective component so that amplitude maxima occur. Additional variations will become apparent to those skilled in the art from the following description of the invention in relation to the illustrated examples that follow.